JPS62103526A - Knocking sensor - Google Patents

Abstract

PURPOSE:To obtain the resonance frequency only of fundamental vibration by removing sub-resonance generated by cavity resonance, by providing a sound absorbing material in the housing of a sensor. CONSTITUTION:A sensor is fixed to an engine by mounting the screw part 3 integrally formed to the lower part of a housing 1 to the screw hole of the engine and the vibration of the engine is transmitted to a vibration plate 4 through the screw part 3, the main body of the housing 1 and the projection 2 provided to the inner bottom part of the housing 1. As a result, the vibration plate 4 is integrated with a piezoelectric element 5 to generate mechanical flexural oscillation and the electric signal corresponding to vibration is generated between the electrodes provided to the piezoelectric element 5. When a porous sound absorbing material is provided to the gas between the inner bottom surface of the housing 1 and the vibration plate 4, an incident sound wave enters the hole of the sound absorbing material 12 or the gap and, when said sonic wave is further ready to propagate through a material, the energy thereof is lost by flow resistance caused by viscosity to the vibratory flow of air. Therefore, subresonance due to cavity resonance is removed and the resonance frequency only of the fundamental vibration of a vibration detecting body can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention detects engine block vibration and determines the presence or absence of engine non-king based on the vibration waveform to control ignition timing in order to improve fuel efficiency. This invention relates to a knocking sensor used in a knocking control system.

[Conventional technology]

The conventional knocking sensor shown in FIGS. 2 and 3 is used by fixing the threaded part 3 of the housing 1 to the engine, and when the engine vibrations are transmitted to the housing 1, the diaphragm 4 and piezoelectric element 5 vibrate. As a result, an electric signal corresponding to the vibration is generated between the electrodes of the piezoelectric element 5. This electrical signal is taken out to the outside via the terminal 7, and since the piezoelectric element 5 bends the most at the resonance frequency (for example, in Japanese Patent Laid-Open No. 59-145928), the output shown in FIGS. 4 to 7 is obtained. The frequency characteristics of the voltage can be obtained.

[Problem that the invention seeks to solve]

However, the conventional knock sensor described above has a problem in that the frequency characteristics of the output voltage may generate an abnormal sub-resonant voltage including near the resonant frequency, as shown in FIGS. 4 to 7.

This is considered to be because a phenomenon similar to cavity resonance, which is already used to increase the sound pressure of the piezoelectric buzzer, occurs in the cavity 11, and this has a negative effect on the diaphragm 4 and the piezoelectric element 5.

SUMMARY OF THE INVENTION The present invention aims to eliminate the above-mentioned conventional problems, and aims to eliminate sub-resonance caused by cavity resonance and obtain a resonant frequency of only the fundamental vibration of a vibration detector.

[Means for solving problems]

Therefore, the present invention provides a knocking sensor having a sealed structure in which a vibration detector is fixed in a housing and a cover body such as an insulating connector or a metal case is provided at the open end of the housing, and a sound absorbing material is provided inside the housing. The present invention provides a knocking sensor characterized by the following.

[Effect]

As a result, the energy of cavity resonance generated in the cavity is absorbed by the sound absorbing material.

〔Example〕

The present invention will be described below with reference to embodiments shown in the drawings.

In FIG. 1, reference numeral 1 denotes a metal housing with an open end, and a protrusion 2 is formed approximately at the center of the inner bottom of the housing 1. As shown in FIG. Further, the outer peripheral surface has a hexagonal surface like a bolt. Reference numeral 3 denotes a threaded portion integrally formed on the lower outer bottom of the housing 1, and this threaded portion 3 is attached to a threaded hole of the engine. Reference numeral 4 denotes a metallic disc-shaped diaphragm, and a hole is formed in the center of this diaphragm 4. The periphery of the center hole of this diaphragm 4 is welded and fixed to the tip of the protrusion 2 of the housing 1. 5 is a disk-shaped piezoelectric element, and a hole is formed in the center of this piezoelectric element 5. This piezoelectric element 5 is adhesively fixed to the diaphragm 4. Reference numeral 6 denotes a connector made of an insulator that serves as a lid, and is fixed to the open end of the housing 1, and a recess 6a is formed in the lower surface of the connector 6.

A metal terminal 7 is embedded and fixed through the inside of the connector 6, and extends to the center of the recess 6a on the lower surface of the connector 6.

8 is a wire of a signal line, and the lower end of the terminal 7 and the piezoelectric element 5
It is soldered to the silver electrode formed on the surface.

Reference numeral 9 denotes an annular washer, which is attached to the stepped portion of the housing 1 and serves as a stopper for the connector 6. 10 is an O-ring for waterproofing, and 11 is a cavity inside the housing 1, which has a sealed structure. Reference numeral 12 denotes a porous sound absorbing material, which is attached to the inner bottom surface of the housing 1 with or without adhesive through a gap with the diaphragm 4.

In the knocking sensor shown in FIG. 1, a threaded portion 3 integrally formed at the bottom of a housing 1 is attached and fixed to a threaded hole in an engine. Engine vibrations are transmitted to the diaphragm 4 via the threaded portion 3, the main body of the housing 1, and the protrusion 2 on the inner bottom of the housing 1. As a result, the diaphragm 4 and the piezoelectric element 5 work together to cause mechanical deflection vibration, and the piezoelectric element 5
An electrical signal corresponding to the vibration is generated between the electrodes provided on the

This electrical signal is taken out to the outside via the wire 8 and the terminal 7.

However, in the conventional knocking sensor shown in FIGS. 2 and 3, cavity resonance occurs in the internal cavity 11 of the housing l near the resonance frequency of the diaphragm 4 and the piezoelectric element 5 that generate the original output signal. When this adversely affects the diaphragm 4 and the piezoelectric element 5, sub-resonance as shown in FIGS. 4 to 7 occurs, and this sub-resonance has a major disadvantage in that it deteriorates the knocking detection function.

In order to eliminate the above-mentioned drawbacks, the knock sensor of this embodiment has the following features:
As shown in FIG. 1, a porous sound absorbing material 12 is provided in the gap between the inner bottom surface of the housing l and the diaphragm 4. This sound absorbing material 12 has many small holes and gaps extending from the surface of the material toward the inside, and the sound waves incident on the surface of such material,
When it penetrates into holes and gaps and then attempts to propagate through the material, it loses its energy due to flow resistance due to viscosity against the oscillating flow of air.

Figure 8 shows the experimental results of the same sensor with sound absorbing material provided (solid line) and without sound absorbing material (broken line).
In the case without the sound absorbing material, secondary resonance occurs as shown by the broken line, whereas in the case with the sound absorbing material, there is no secondary resonance as shown by the solid line, and an output voltage of only a single resonant frequency is generated.

Figure 9 shows the change in secondary resonance between room temperature (dashed line) and 120°C (solid line) for the same sensor without sound absorbing material.As the temperature rises from room temperature to 120°C, The resonance shifts to a frequency that is about 1.15 times higher. Assuming that this change in cavity resonance frequency is a change in sound speed, it almost matches the calculated value. From the above experimental results, it can be concluded that the sub-resonance is due to the cavity resonance of the cavity. The effect of the cavity resonance often appears at frequencies above about 10 kHz, and the effect of providing a sound absorbing material is significant for knocking sensors in which the resonance frequency of the vibration detector 4.5 is about 10 kHz or above.

Suitable sound absorbing materials include porous soft resin, foamed rubber, and fiber aggregates such as cotton.

Note that in the configuration shown in FIG. 1, the sound absorbing material 12 is
Although the sound absorbing material 12 is provided in the gap between the inner bottom surface of the base 9 and the diaphragm 4, the sound absorbing material 12 may be provided on the surface of the base 9 as long as it has the structure shown in FIG.

In addition to what has been described above, in the embodiment, the sound absorbing material 12 is provided only on one side of the vibration detecting body, but the sound absorbing material 12 may be provided on both sides.

Alternatively, a recess may be formed in the area where the sound absorbing material is to be provided, and the sound absorbing material may be stored in that area.

Furthermore, instead of the connector 60, a lid such as a metal case may be provided at the open end of the housing 1.

[Effects of the Invention] As described above, in the present invention, the energy of the cavity resonance generated in the cavity in the housing is absorbed by the sound absorbing material, the sub-resonance due to the cavity resonance is removed, and the fundamental vibration of the vibration detector is This has the excellent effect of being able to obtain a unique resonance frequency.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view showing one embodiment of the sensor of the present invention;
3 and 3 are vertical sectional views showing two examples of conventional sensors, FIGS. 4 to 7 are frequency-output voltage characteristic diagrams of the conventional sensor, and FIG. 8 is frequency-output voltage characteristic diagrams of the sensor of the present invention.
Output voltage characteristic diagram, Figure 9 shows the above conventional sensor at room temperature and 12
It is a frequency-output voltage characteristic diagram at 0°C. ■... Housing, 4.5... Vibration plate and piezoelectric element constituting the vibration detection body, 6... Connector 212... Sound absorbing material. Representative Patent Attorney Takashi Okabe 7 Figure 11 Figure 2 Figure 3 You, Country Section 15-DC Side Hanaya - Former N Chen Number Figure 8 Zhou Ying Figure 9

Claims (1)

[Claims] A knocking sensor having a sealed structure in which a vibration detector is fixed in a housing and a cover body such as an insulating connector or a metal case is provided at an open end of the housing, characterized in that a sound absorbing material is provided inside the housing. knocking sensor.